This invention relates generally to an improved turbocharger design. Turbochargers in general are well known in the art for supplying relatively high pressure air, commonly referred to as charge air, to the intake manifold of an internal combustion engine, such as a reciprocating piston engine of the type commonly used to power automobiles, trucks, buses and the like. Typically, the turbocharger comprises a turbine housing connected for receiving exhaust gases expelled from the engine and configured for guiding those exhaust gases into driving communication with a rotating turbine wheel. The turbine wheel is carried by a rotatable shaft connected to a compressor impeller within a compressor housing. The turbine wheel thus rotatable drives the compressor impeller which in turn draws ambient air into the compressor housing for compression and discharge in the form of charge air supplied to the intake manifold of the engine.
Typically the rotating shaft in a turbocharger is capable of being driven at relatively high rotational speeds, such as on the order of about 120,000 rpm or more. Thus, the shaft connecting the turbine wheel and compressor impeller must be supported by suitable journal bearings and thrust bearings within a center housing connected between the turbine housing and the compressor housing. Normally, lubricating oil from the engine is commonly pumped under pressure to the turbocharger center housing for lubricating the shaft bearing so as to prevent excessive bearing heating and wear.
Turbocharged engines are highly advantageous when compared with conventional naturally aspirated engines in that substantially denser air can be delivered to the combustion chamber or cylinders of the engine. This increased air density or mass permits the engine to be operated at substantially increased levels of peformance and power output, and frequently with greater efficiency. In this regard, however, it is necessary to control the operation of the turbocharger so that the charge air is supplied to the engine only on demand at a pressure level not exceeding a predetermined design limit. While a variety of control schemes are known, it is conventional to provide a passage for bypassing exhaust gases around the turbine wheel and including a so called wastegate valve for opening and closing this bypass passage.
As turbochargers find increasing use on smaller and smaller automobile engines, it is necessary that they be lighter, more compact, and less costly to build. Simply scaling down a conventional turbocharger has not proven to be an effective, cost efficient way of producing these smaller turbochargers.